1. Field of the Invention
The invention relates to methods and apparatus for completing lateral channels from existing oil or gas wells. More particularly, it relates to improved methods and apparatus for penetrating the well casing of an existing well at a given depth, and completing one or more laterals at that depth.
2. Description of Related Art
Oil and gas are produced from wells drilled from the earth surface into a hydrocarbon “payzone.” Once a well is drilled, it essentially is a hole in the earth extending from the earth surface downward several hundred or thousand feet into or adjacent a hydrocarbon payzone. The thus drilled hole generally is not very stable because, among other things, its earthen walls are highly subject to erosion or shifting over time, whether due to the flow of hydrocarbons to the surface, or other natural causes such as water erosion from rain or flooding. This is especially of concern considering many oil and gas wells stay online for several or tens of years, or longer.
To impart stability to a drilled well, it is conventional to encase the well bore with a casing material, typically made from steel. The steel well casing essentially is a cylindrical-walled pipe having an OD somewhat smaller than the ID of the well bore drilled from the earth surface. The well casing is placed down in the well bore, typically in discrete sections which are secured or otherwise joined together as is known in the art. Once the well casing is in place centrally within the earthen well bore, it is conventional to fill in the thus-defined annular space between the well casing and the well bore with cement.
The resulting construction is an oil or gas well consisting of a cement-encased steel pipe extending from the earth surface down into a hydrocarbon payzone from which hydrocarbons (oil and/or gas) can be extracted and delivered to the surface via conventional techniques. This steel pipe, also called the well casing, defines an inner bore or passageway for the delivery of hydrocarbons to the surface. The described construction has proven useful for decades to produce oil or gas from hydrocarbon payzones located at, or which empty into, the base (bottom end) of the well casing. However, once these payzones dry up, either the well must be abandoned or it must be treated in order to make it productive and profitable once again.
There are several conventional treatment techniques for revitalizing an otherwise unproductive well. Two of the most common are referred to as acidizing and fracturizing. Both of these techniques are designed to increase the adjacent formation's porosity by producing channels in the formation allowing hydrocarbons to flow more easily into the perforated well bore, thereby increasing the well's production and its value. However, the success of these operations is highly speculative and both are very expensive and require dedicated heavy equipment and a large crew.
A more efficient technique for stimulating a diminished production well is to drill a hole through the well casing at a depth below the earth surface, and then to bore a lateral channel through the predrilled hole into an adjacent payzone using a high pressure water jet nozzle (blaster nozzle). Various techniques and apparatus for boring lateral channels downhole are known in the art, for example as described in U.S. Pat. Nos. 6,530,439, 6,578,636, 6,668,948, and 6,263,984, the contents of all of which are incorporated herein by reference. Generally, an elbow or “shoe” is used downhole to redirect a cutting tool fed from the surface along a radial or lateral path at a depth at which a lateral channel is to be completed. The cutting tool is directed laterally against the well casing to cut or drill a small hole through the casing and the cement encasement beyond, and is then withdrawn to make way for a separate blaster nozzle and associated high pressure water hose that must be snaked through the previously drilled hole. This technique, which is simple to describe, in practice can be difficult to perform, with uncertain or irreproducible results.
For one thing, often it is difficult and sometimes even impossible to determine with certainty that a hole actually has been cut through the casing and the cement encasement. Also, even assuming a successfully cut hole, it can be extremely difficult to ensure accurate alignment of the elbow or downhole shoe in order to direct the blaster nozzle through the previously cut hole. For example, the shoe may be jerked or moved during withdrawal of the cutting tool or insertion of the blaster nozzle. In addition, it is extraordinarily difficult, if not impossible in most cases to realign the shoe with a previously cut hole if the shoe alignment is accidentally shifted, or if it must be shifted (e.g. to drill another hole) subsequent to drilling the hole in the casing but prior to feeding the blaster nozzle through the hole. Often it is impossible to know at the surface if the alignment of the shoe with the previously drilled hole has been disturbed and needs readjustment.
There is a need in the art for a method of perforating the well casing (and annular cement encasement) at depth within an existing oil or gas well, wherein the precise alignment of a downhole tool need not be exactly maintained to ensure a subsequently introduced boring tool, such as a high pressure blaster nozzle, can be directed through the previously made perforation to bore a lateral channel or channels therefrom.